MESOSCALE EDDY STRUCTURE AND HORIZONTAL BIOGEOCHEMICAL VARIABILITY FROM AUTONOMOUS OBSERVATIONS IN THE NORTH PACIFIC SUBTROPICAL GYRE
Mesoscale eddies move westward across subtropical gyres affecting the structure and function of pelagic ecosystems and influencing the observations at Eulerian sampling sites as Station ALOHA. To understand the impact of these vortices on the ecosystem processes in the North Pacific Subtropical Gyre, we employed autonomous underwater gliders to sample across mesoscale eddies while they were passing north of the Hawaiian Islands. Oceanographers routinely use autonomous observations to study pelagic ecosystems, but these measurements have been biased toward the quantification of stocks, as chlorophyll or particle concentration, rather than rates, as the production and consumption of these stocks. To overcome this problem, we used a recently proposed method to calculate gross photosynthesis from diel cycles of dissolved oxygen that provided rate estimates with a horizontal resolution of tens of kilometers. Three gliders were deployed across different eddies and characterized the horizontal hydrographic changes due to mesoscale dynamics, including the occurrence of thin diagonal filaments with positive salinity and oxygen anomalies. The concurrent biogeochemical observations show that the vertical displacement of isopycnal surfaces due to geostrophic motions drive changes in the lower portion of the euphotic zone, below the depths that are routinely observed by satellites. Furthermore, we observed that rates are horizontally more variable than stocks, and that the two do not correlate as we would have expected.
Barone, B., University of Hawaii at Manoa, USA, email@example.com
Nicholson, D. P., Woods Hole Oceanographic Institution, USA, firstname.lastname@example.org
Karl, D. M., University of Hawaii at Manoa, USA, email@example.com
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